There are various kinds of pressure sensitive recording sheets known for transmitting information wherein a color-forming reaction between a plurality of chromogenic materials, for example, between an electron-acceptive reactant material (hereinafter referred to as "color acceptor") such as activated clay, phenol-formaldehyde condensate, polyvalent metal salts of aromatic carboxylic acids, etc. and an electron donative chromogenic material (hereinafter referred to as "color former") such as Crystal Violet lactone, N-benzoyl leucomethylene blue, etc. is utilized and pressure serves as a medium to provide expected color images.
Any of these known pressure sensitive recording sheets comprise (i) a top sheet (CB) comprising a substrate having a surface coated with a layer containing microcapsules each containing a color former prepared by the known coacervation method, interfacial polymerization method or in-situ polymerization method and (ii) a bottom sheet (CF) having a surface coated with a layer containing a color acceptor capable of reacting with said color former to cause color development, and if necessary, in addition to said two sheets, (iii) a middle sheet (CFB) having a surface coated with a layer containing the foregoing microcapsules and another surface coated with a layer containing a color acceptor, and the top sheet and at least one of the bottom and middle sheets are used in combination.
Other than the above pressure sensitive recording sheets, there has been proposed a so-called self-contained type pressure sensitive recording sheet comprising a substrate having a surface provided with a two layers-stacked structure or a mixed layer structure including the foregoing microcapsules and a color acceptor.
There has been also proposed a self-contained type pressure sensitive recording sheet set comprising the foregoing self-contained type pressure sensitive recording sheet, the rear surface of which is coated with a layer containing the foregoing microcapsules, the foregoing bottom sheet (CF) or/and the foregoing middle sheet (CFB) in combination.
For the preparation of these pressure sensitive recording sheets in general, an appropriate aqueous coating composition is applied onto the surface of a substrate with the use of a large coater, which is then followed by drying.
Other than this method, for the preparation of a pressure sensitive recording sheet having a layer containing microcapsules each containing a color former, there has been proposed a method wherein an ink composition containing said microcapsules is prepared, and the resultant ink composition is spot-printed onto a substrate by means of an appropriate printer such as Business-form printer, followed by drying.
This method is more advantageous in comparison with the former method using a large coater from the viewpoint that it is possible to prepare such a pressure sensitive recording sheet that has a surface with partially varied color tones as desired and it is also possible to prepare such a pressure sensitive recording sheet that can exhibit desired characteristics upon its use.
On the contrary, there are disadvantages of this method: (a) the amount of microcapsules to be applied is apt to become insufficient and because of this, the resulting pressure sensitive recording sheet is poor in color development (which means that it is difficult to provide a desirable high density color image), (b) unevenness is apt to be caused on a printed coat formed on a substrate, and (C) the insufficiency of the amount of microcapsules applied and the uneven coating are apt to jointly occur and as a result, the resulting pressure sensitive recording sheet provides undesirably unclear color images.